The Secretary General's line of once being called "Mr. One Shot" in Final Wars is a reference to an action film his actor Akira Takarada did years ago titled 100 Shot, 100 Killed.
The infamous leap Godzilla does in Godzilla vs. Megaguirus? A reference to Tsutomu Kitagawa's involvment in the Super Sentai series. With the exception of Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack, Kitagawa was the man in the Godzilla suit throughout the Millennium series.
In Godzilla vs. Hedorah, Godzilla crosses his arms in a "+ " position. This same pose was made famous by Ultraman, whenever he fires off his trademark Specium Beam to finish off monsters.. Godzilla's (then) suit actor, Haruo Nakajima, played several Monsters of the Week in the original Ultraman series (one of them, Jiras, was in fact based from an older Godzilla suit, except with a large frill).
Nakajima's protegé was Bin Furuya a.k.a. Ultraman.
Akihiko Hirata wears an eyepatch in Ebirah, Horror of the Deep, in allusion to his most famous role as the eyepatch-wearing Dr. Serizawa in the original Godzilla.
The mini subs used in GMK are named Satsuma, in reference to actor Kenpachiro Satsuma, who played Godzilla from 1984 to 1995.
The character played by Kumi Mizuno in Godzilla Final Wars is named Namikawa, in reference to her earlier role as Miss Namikawa in 1965's Invasion of Astro-Monster.
Executive Meddling: Ishiro Honda, the director of the first film and many other Toho kaiju movies, preferred science fiction/alien invasion movies (like The Mysterians or Gorath) to kaiju efforts, but the monster movies were so successful that he didn't really have a choice. This is not necessarily a bad thing, as he still made excellent movies, but Honda's non-kaiju movies are often unfairly overlooked. This would explain why some of his entries had space monsters or alien invaders or both for Godzilla to fight. One of his movies even takes place on Planet X.
Also, Shusuke Kaneko originally wanted to use Anguirus and Varan in a Godzilla movie he was directing. However, the executives at Toho Studios told him he had to use two more popular monsters. The end result? Godzilla, Mothra, King Ghidorah: Giant Monsters All-Out Attack.
Akira Kurosawa, one of the most respected filmmakers of the 20th century, wanted to direct a Godzilla movie, but Toho didn't want to spend the money (as Akira was known to go overbudget and himself cost a lot to direct a film in addition to the Special Effects cost).
Franchise Killer: Tri-Star's 1998 "adaptation" was almost this and from what reports said about Dean Devlin and Roland Emmerich's attitude towards it, this may have been their intent.
Keep Circulating the Tapes: Several films, notably those from the Showa era, have fallen into this. Granted, Sony and Tristar have rereleased said films on DVD, but these releases have since gone out of print. Fortunately, with companies like Classic Media and Kraken Releasing, this issue seems to be turning on its head.
The original Japanese cut of King Kong vs. Godzilla has, so far, never been released in the US, and the current DVD release the movie did receive from Universal only contains the American cut. King Kong Escapes also shares this fate.
The worst example would be The Return Of Godzilla, despite the movie getting a theatrical release in America. The English version of the movie received a release on VHS that has since gone out of print... and that's about it. For some unknown reason, no company has bothered to license The Return of Godzilla and release either the Japanese version, the American version, or both on DVD or possibly Blu-Ray.
Godzilla vs. Megalon has managed to avert this, but in the worst way possible. Media Blasters, who previously released Destroy All Monsters, was set to release Godzilla vs. Megalon on DVD and Blu-Ray under their Tokyo Shock label. However, there was a problem: their DVD and Blu-Ray release of Destroy All Monsters contained special features that weren't approved by Toho. This resulted in the release going out of print, as well as the DVD and Blu-Ray release of Godzilla vs. Megalon being put on hold while Media Blasters and Toho sort the issue out. As a sort of placeholder, Media Blasters did release the movie on DVD... a barebones DVD with no special features whatsoever. As of this edit, only the barebones DVD release (which is currently out of stock on Amazon.com) remains available, and the Blu-Ray has yet to be released. Media Blasters have announced plans to release a "Special Edition" of the DVD that contains the planned special features, along with the Blu-Ray version that contains the special features as well, but seeing as how it's now 2014 at the time of this edit and the Special Edition DVD and Blu-Ray still remain in limbo, it's doubtful there were even plans in the first place.
Terror of Mechagodzilla was at one point another case of this; the film has only been released to home video twice, and the first release was when Tri-Star had the rights to the franchise back in the 1998-2002 area, and as with all of those releases it has since gone out of print. As well, no Godzilla films have been released to Netflix as of March 2014 (though this may change when the Legendary remake lands this May). For a long time, it seemed the only way to watch Terror was to either happen to have a copy of the out-of-print DVD or pirate it onto your computer and watch it there. Thankfully, Classic Media has since released the movie on DVD.
Back when DVD didn't exist yet, this trope was sadly played straight with the Heisei Godzilla movies for a while. The last movie to be officially released in the US was Godzilla vs. Biollante, which, while not released theatrically like its predecessor, was given a VHS release along with airings on cable television. After that, however, following Godzilla movies weren't given any official release in the states whatsoever, and the only way to watch them was by importing. It wasn't until both DVD and the 1998 remake came around that every Godzilla movie from vs. King Ghidorah to vs. Destoroyah was finally given an official release.
The Japanese version of King Kong vs. Godzilla has not been released on DVD outside of Japan.
Playing Against Type: King Ghidorah, usually a villain, is The Hero in GMK. That's not the only occasion where a monster has switchedmoralities, but given that he otherwise varies between being a force of nature and outright evil, it's very notable.
Prop Recycling: Older Godzilla suits were often used in the latest movie for certain scenes to keep the current suit as undamaged as possible. This was often done for scenes featuring Godzilla in/under the water.
Trope Namers: Godzilla was the source of the following trope names:
What Could Have Been: Godzilla was originally going to be a giant octopus, then later a giant fire-breathing gorilla, before Toho decided to make him the radioactive dinosaur we all know and love today.
Likewise, Godzilla himself was originally going to be portrayed via stop motion animation. The idea was quickly dropped when the filmmakers realized it would be too time-consuming.
King Kong vs. Godzilla eventually came out of Willis O'Brien's desire to make a King Kong vs. Frankenstein.
Toho initially wanted to shoot on location in Sri Lanka, but since the rights to Kong slashed the budget, they resorted to shooting on their own Oshima Island.
Frankenstein Conquers The World was originally going to be Frankenstein vs. Godzilla. The idea was dropped when Toho realized what a one-sided match up it was, coupled by the fact that by the time they had thought up the movie, Godzilla had turned from villain to hero (and Frankenstein would've obviously been the hero of the story). The movie wasn't entirely scrapped, however: Toho simply replaced Godzilla with Baragon.
Toho was going to loan Godzilla out to Tsuburaya Productions for the studio's 10th anniversary. The resulting movie was going to be called Godzilla vs. Redmoon, in which two monsters — Redmoon and Erabus — appear in Japan. The military brings them together in the hopes that they will fight and destroy each other, but it turns out the beasts are male and female of the same species, and they mate! They hatch a little monster named Hafun, whom is unfortunately killed by an entrepreneur trying to capture him. When Redmoon and Erabus predictably go berserk, Godzilla appears and engages the two in battle. The movie was all set to be made when it was abandoned for reasons unknown. It would eventually be heavily reworked into a stand-alone movie without Godzilla, called Daigoro vs. Goliath.
Henry G. Saperstein, the American producer who helped with Monster Zero, Frankenstein Conquers The World and War Of The Gargantuas, liked the Gargantuas so much that he suggested a Godzilla vs. Gargantua movie. Unfortunately, the idea never got passed the planning stage, and it's unknown if Godzilla was going to face Gaira, Sanda, both or a new Gargantua entirely.
When Toho was trying to bring Godzilla back during the late '70s, they decided to cash in on the supernatural/Satanic craze that most horror movies were into at the time (like The Omen and The Exorcist) with Godzilla vs. the Devil, a joint production between Toho and UPA Productions. Mankind's sins begin to take physical form, creating monsters that resemble a spider, a fish and a bird. Godzilla arrives and defeats the demons, but Satan appears to battle Godzilla himself. One can only imagine how a showdown between the King of the Monsters and the Prince of Darkness would've turned out.
One of the more interesting ideas was Godzilla Vs the Asuka Fortress. The concept for this production was penned by longtime series writer Shinichi Sekizawa along with producer and then Toho president Tomoyuki Tanaka. Despite what the title might suggest, Godzilla's rival in this production was to be a humanoid robot constructed by the Self Defense Force that was either part of the "Asuka Fortress" or it was to be the title character itself. Details are unfortunately very scarce (the only well known thing being that the film's plot dealt with a government revolt), and among those things uncertain is what type of role Godzilla was to play. Due to the revolt within the government, which was certainly an interesting story vehicle on the part of writer Sekizawa, it's quite possible that the "Asuka Fortress" was going to be manned by a rogue part of the government and the movie could have seen Godzilla slip into his hero persona to defeat it. In fact, it's quite possible that this movie would have continued the Showa series, although given the lack of details it's hard to say for sure either.
A concept proposed by writer Ryuzo Nakanishi in June of 1978, titled King of the Monsters: Rebirth of Godzilla, with the first portion of the title in English and the second in Japanese, the production was to be a remake of the original 1954 Godzilla film. The concept struck a cord with producer Tomoyuki Tanaka, as a more complete draft was commissioned. This second stage of production had both Nakanishi and writer Akira Murao at work on developing the concept, and was submitted on October 22nd, 1978. Jun Fukuda was set to direct the movie, but for whatever reason the project never came to pass. Given the very late draft submission, it's also worth noting that this film was possibly going to be slated for a 1979 release instead, unless the project itself ran behind schedule early on and was axed for that reason.
Right after Godzilla vs. Biollante, Toho decided to bring back their second biggest star, Mothra, in her own movie: Mothra vs. Bagan. The two creatures were to engage in a series of battles across the globe before Mothra and the Mothra larva joined forces to defeat Bagan in a fight to the finish. Aside from Super Godzilla, this unused script is probably what Bagan is best known for.
Would you believe that the film Gunhed started life as a Godzilla project?
Also planned was a '90s remake of King Kong vs. Godzilla, for Toho's 60th birthday. The idea was dropped when Toho discovered that rights to Kong had become ridiculously expensive since 1962.
Even sooner than that, There were plans for a direct sequel back in the 60's. Following the immense success of the first film (which when adjusted for inflation would be the highest grossing Godzilla film of all time), it's not surprising that the first concept considered for the next Godzilla movie was one that pitted the two monsters against each other again. Literally titled Continuation: King Kong vs. Godzilla, the proposal for this project was written by Shinichi Sekizawa, who also worked on the previous film, and the draft was submitted in 1963. Unfortunately, the concept never got past the proposal stage, and a more fleshed out script was never commissioned while Sekizawa's ideas for the sequel remain mostly unknown.
Apparently, a few monsters were cut from the final version of Final Wars; Kiryu, Oodako, Gorosaurus, Mothra Larva, and King Ghidorah to be precise.
Kiryu, Gorosaurus, and King Ghidorah, were all replaced by Gotengo, Zilla, and Kaiser Ghidorah respectively.
Daiei actually approached Toho on making a Godzilla vs Gamera movie. Which Toho rejected. That sound you hear is your fandom crying.
As said, Famed director, Akira Kurosawa once expressed a desire to direct a Godzilla movie, but was turned down by the good people at Toho, who were terrified by the thought of the budget that might be required to realize Kurosawa's vision.
The original version of Dr. Yamane (Gojira) was going to be more of a caped corny villain who wanted Godzilla to leave. Even going so far as to sabotage operations against him. Thankfully all but his desire to have Godzilla live, to study for the good of mankind, were removed over time.
In 1994, an attempt to make a different American Godzilla movie was made:
It was to have Industrial Light and Magic provide effects and have Godzilla fight an alien creature called The Gryphon. ILM ended up dropping out. But even with Stan Winston offering his services (and even designing both monsters), the movie was never made due to Sony freaking out at the $120 million budget.
King Kong, and Zilla - The two american kaiju were hinted to be in the game in an interview. However they never made to the final cut of the game; King Kong due to rights issues with Universal and Zilla due to lack of popularity.
Fire Lion, The Visitor, and Lightning Bug - The other conceptualized "new" monsters to be voted into the game. However they all lost to Krystalak and Obsidius.
Mechani Kong - Same reason as Kong.
Gamera - Rights issues with Daiei.
Bagan - Dropped in favor of Varan due to Simon Strange liking Varan moreso.(Guy never gets a break huh folks?)
Word of Saint Paul: Haruo Nakajima, the original actor who played Godzilla, believes that the Showa (1955-1975) incarnation of Godzilla is female. However, according to Toho Studios, all incarnations of Godzilla to date have been male (yes, even the remake version).